The invention relates to a procedure for manufacturing a composite element out of a truncated, cone-shaped, fire-proof ceramic insert, which is enclosed by a metal jacket, as well as to a device for executing the procedure.
Such composite elements can be used in gas rinsing systems during pig iron and steel production. During the treatment of molten metals in secondary metallurgy, inert gases such as argon or nitrogen are blown into the melt through gas rinsing systems as an important step. The mild to intensive rinsing of the melt better dissolves added alloys, and the composition and temperature of the melt are balanced out. The gas rinsing systems can be incorporated in the floor or lateral wall of the metallurgical vessel, for example a steel treatment pan. Numerous embodiments are known for gas rinsing systems.
Gas rinsing stones normally consist of a gas supply device, a gas distribution area, a ceramic rinsing cone and, if necessary, a metal jacket. The gas rinsing stone is predominantly incorporated into a perforated brick in the fire-proof lining, for example into the pan floor or a sleeve, which are in turn walled or banked in the fire-proof lining. So that the rinsing stone can be replaced from outside during the pan campaign, use is usually made of a truncated, cone-shaped rinsing stone cone in which the face with the smaller diameter is directed at the interior of the pan.
There are different basic designs to enable the throughput of gases through the rinsing stone. For example, changes are introduced in the structural design of the ceramic part, or cauterization materials are added, which bring about an increased porosity during ceramic firing, or the ceramic insert is provided with fine gaps or channels in an otherwise impervious ceramic body, or gas is supplied through an annular gap between an impervious ceramic cone and an encasing metal jacket. Combinations of various embodiments are also possible.
In order to generate fine gas bubbles for stirring the molten metal, embodiments of gas rinsing stones are preferred in which the ceramic insert consists of porous, fire-proof material, or has fine channels with a small diameter or slits (xe2x80x9cdirected porosityxe2x80x9d). In this case, it is required that the metal jacket fits uniformly tight against the ceramic insert over the entire circumference and its entire length. If at all possible, gas is to be prevented from passing between the metal jacket and wall of the ceramic insert. Even given progressive wear over time, gas is to pass through the interior of the ceramic insert in as a distribution defined as possible. A nonuniform passage of gas at the edge of the ceramic insert must be avoided if at all possible.
Known from DE 196 53 747 A1 is to heat the metal jacket using an induction coil secured in a bell type furnace and then shrinking it onto the ceramic insert. The disadvantage is that placing the glowing metal jacket on the ceramic insert at excessive temperature differences can cause cracks to form in the structure of the ceramic insert. On the other hand, the temperature difference cannot be too slight, since the objective is to reliably shrink the metal jacket onto the ceramic insert. To this end, DE 196 53 747 A1 proposes that the metal jacket encases the ceramic insert at a distance without contacting it inside a bell type furnace with induction coil, and heating it via radiated heat. The metal jacket and ceramic insert are to be brought together right after the metal jacket has been heated.
Heating takes place inside an inductor by means of inductive heating in the procedure known from DE 40 21 259 A1 as well. Only the outside jacket can be heated inductively. The inner ceramic part is positioned inside the metal jacket using a hoisting device.
The object of the invention is to avoid the disadvantages while shrinking a separately heated, hot metal jacket onto a colder ceramic insert, and achieve a uniform bond between the metal jacket and ceramic insert in a simple procedure, without inductively heating the metal jacket, and without using mechanical devices to bring it together with the ceramic insert.
The object is achieved according to the invention in a procedure of the kind mentioned at the outset by first sliding the fire-proof insert into the metal jacket, heating the conical metal jacket with the opening having the smaller diameter facing down on a substrate from outside, wherein the ceramic insert and metal jacket always remain in contact, and heating to a temperature high enough that the ceramic insert shifts downward into the composite position solely under its own weight with the metal jacket expanding.
It was found that no additional forces need to be exerted by means of a mechanical device to press the ceramic insert into the metal jacket while the latter expands open. This is accomplished solely by the weight of the ceramic insert.
As a result, the metal jacket exerts a particularly uniform compressive stress on the ceramic insert after cooling. This is advantageous, since the metal jacket can in this way support the fire-proof ceramics during use as a gas rinsing stone, which reduces the susceptibility to cracking of the rinsing stone, and ensures that the rinsing gas only passes through the stone into the melt on the prescribed path.
One advantageous embodiment of the procedure can be characterized by the fact that the metal jacket with the ceramic insert accommodated therein rotates around the perpendicular axis during the heating process. The uniform rotation at a defined distance from the heating device achieves a particularly uniform heating of the metal jacket. The heating device preferably consists of numerous burner flames, which can be distributed over the height of the metal jacket. In addition, burner flames can be distributed over the circumference of the metal jacket.